Good questions. It has been discussed before.
MTP is what I am used to - but I am not wedded to that particular protocol. You will note that the second link above suggests simply syncing via WiFi.
For my L5, I plan to put music on the µSD card, which means that I could load the card by putting the µSD card in the host computer, loading it up and then moving the µSD card to the L5.
The outstanding question is whether, via the USB interface (as yet unspecified?), the eMMC drive will be exposed in some way.
I suspect that the answer right now is: lower priority but it’s on the radar.